1. Field of the Invention
The apparatus and method of the present invention relate genrally to removing airborne particles by electrostatic precipitation, and more particularly to treating electrically charged airborne particles to reduce deposition of the particles on walls and other exposed surfaces in an enclosed area.
2. Description of the Prior Art
The removal of solid or liquid airborne particulate contaminants by electrostatic precipitator air cleaning systems is quite well known and widely practiced in commercial and industrial environments. It has been shown that such systems can capture up to 99% of all airborne particulates from 0.01 micrometer to about 100 micrometers in diameter. Included within this range are respirable fraction particles that are most damaging to the human lungs, since they tend to bypass the bodys natural filters and defense mechanisms.
The operation of such electrostatic precipitator air cleaners, such as the popular two-stage Penney type, is well known in the art and only need briefly be described. Such a precipitator operates on the principle of charging contaminants electrostatically and then collecting the charged particles on a ground plate in an electrostatic field. Contaminated air drawn into the precipitator, by a fan or blower, may be screened by a mechanical prefilter which removes large airborne particles from the airstream. The air then passes through an ionizer where it is subjected to an intense electrostatic field, which electrically charges all the airborne particles in the airstream. These charged particles next enter the collecting cell where collecting plates of the same polarity as the charged particles repel the charged particles toward plates of ground potential which strip the particles from the airstream. An afterfilter may be included to improve the collection efficiency by trapping any agglomerated contaminants.
It has been a long standing problem that such precipitator air cleaners tend to exhaust an undesirable quantity of electrically charged particles under certain conditions. This problem has been found to be particularly acute in working environments having very contaminated air, such as might be found in manufacturing facilities performing welding and other smoke-producing operations. Moreover, the problem may be aggravated during conditons of low relative humidity. These free electrically charged airborne particles exhausted by the electrostatic precipitator air cleaners tend to be deposited on exposed surfaces, such as walls and shelves, as well as equipment in the working environment, forming a dirty film thereon. It has also been suggested that this precipitated dirt may interfere with the operation of mechanical equipment, resulting in increased wear and equipment failure. Hence a solution has been sought to prevent this particulate build-up on such surfaces.
It has been proposed to add additional mechanical filter stages to the outlet of the electrostatic precipitator air cleaner to trap these charged airborne particles. However, such filters have not proved totally effective, becoming easily clogged and disrupting the precipitator's clean air distribution.